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diff --git a/archival/libarchive/unxz/README b/archival/libarchive/unxz/README new file mode 100644 index 000000000..c5972f6b8 --- /dev/null +++ b/archival/libarchive/unxz/README @@ -0,0 +1,135 @@ + +XZ Embedded +=========== + + XZ Embedded is a relatively small, limited implementation of the .xz + file format. Currently only decoding is implemented. + + XZ Embedded was written for use in the Linux kernel, but the code can + be easily used in other environments too, including regular userspace + applications. + + This README contains information that is useful only when the copy + of XZ Embedded isn't part of the Linux kernel tree. You should also + read linux/Documentation/xz.txt even if you aren't using XZ Embedded + as part of Linux; information in that file is not repeated in this + README. + +Compiling the Linux kernel module + + The xz_dec module depends on crc32 module, so make sure that you have + it enabled (CONFIG_CRC32). + + Building the xz_dec and xz_dec_test modules without support for BCJ + filters: + + cd linux/lib/xz + make -C /path/to/kernel/source \ + KCPPFLAGS=-I"$(pwd)/../../include" M="$(pwd)" \ + CONFIG_XZ_DEC=m CONFIG_XZ_DEC_TEST=m + + Building the xz_dec and xz_dec_test modules with support for BCJ + filters: + + cd linux/lib/xz + make -C /path/to/kernel/source \ + KCPPFLAGS=-I"$(pwd)/../../include" M="$(pwd)" \ + CONFIG_XZ_DEC=m CONFIG_XZ_DEC_TEST=m CONFIG_XZ_DEC_BCJ=y \ + CONFIG_XZ_DEC_X86=y CONFIG_XZ_DEC_POWERPC=y \ + CONFIG_XZ_DEC_IA64=y CONFIG_XZ_DEC_ARM=y \ + CONFIG_XZ_DEC_ARMTHUMB=y CONFIG_XZ_DEC_SPARC=y + + If you want only one or a few of the BCJ filters, omit the appropriate + variables. CONFIG_XZ_DEC_BCJ=y is always required to build the support + code shared between all BCJ filters. + + Most people don't need the xz_dec_test module. You can skip building + it by omitting CONFIG_XZ_DEC_TEST=m from the make command line. + +Compiler requirements + + XZ Embedded should compile as either GNU-C89 (used in the Linux + kernel) or with any C99 compiler. Getting the code to compile with + non-GNU C89 compiler or a C++ compiler should be quite easy as + long as there is a data type for unsigned 64-bit integer (or the + code is modified not to support large files, which needs some more + care than just using 32-bit integer instead of 64-bit). + + If you use GCC, try to use a recent version. For example, on x86, + xz_dec_lzma2.c compiled with GCC 3.3.6 is 15-25 % slower than when + compiled with GCC 4.3.3. + +Embedding into userspace applications + + To embed the XZ decoder, copy the following files into a single + directory in your source code tree: + + linux/include/linux/xz.h + linux/lib/xz/xz_crc32.c + linux/lib/xz/xz_dec_lzma2.c + linux/lib/xz/xz_dec_stream.c + linux/lib/xz/xz_lzma2.h + linux/lib/xz/xz_private.h + linux/lib/xz/xz_stream.h + userspace/xz_config.h + + Alternatively, xz.h may be placed into a different directory but then + that directory must be in the compiler include path when compiling + the .c files. + + Your code should use only the functions declared in xz.h. The rest of + the .h files are meant only for internal use in XZ Embedded. + + You may want to modify xz_config.h to be more suitable for your build + environment. Probably you should at least skim through it even if the + default file works as is. + +BCJ filter support + + If you want support for one or more BCJ filters, you need to copy also + linux/lib/xz/xz_dec_bcj.c into your application, and use appropriate + #defines in xz_config.h or in compiler flags. You don't need these + #defines in the code that just uses XZ Embedded via xz.h, but having + them always #defined doesn't hurt either. + + #define Instruction set BCJ filter endianness + XZ_DEC_X86 x86 or x86-64 Little endian only + XZ_DEC_POWERPC PowerPC Big endian only + XZ_DEC_IA64 Itanium (IA-64) Big or little endian + XZ_DEC_ARM ARM Little endian only + XZ_DEC_ARMTHUMB ARM-Thumb Little endian only + XZ_DEC_SPARC SPARC Big or little endian + + While some architectures are (partially) bi-endian, the endianness + setting doesn't change the endianness of the instructions on all + architectures. That's why Itanium and SPARC filters work for both big + and little endian executables (Itanium has little endian instructions + and SPARC has big endian instructions). + + There currently is no filter for little endian PowerPC or big endian + ARM or ARM-Thumb. Implementing filters for them can be considered if + there is a need for such filters in real-world applications. + +Notes about shared libraries + + If you are including XZ Embedded into a shared library, you very + probably should rename the xz_* functions to prevent symbol + conflicts in case your library is linked against some other library + or application that also has XZ Embedded in it (which may even be + a different version of XZ Embedded). TODO: Provide an easy way + to do this. + + Please don't create a shared library of XZ Embedded itself unless + it is fine to rebuild everything depending on that shared library + everytime you upgrade to a newer version of XZ Embedded. There are + no API or ABI stability guarantees between different versions of + XZ Embedded. + +Specifying the calling convention + + XZ_FUNC macro was included to support declaring functions with __init + in Linux. Outside Linux, it can be used to specify the calling + convention on systems that support multiple calling conventions. + For example, on Windows, you may make all functions use the stdcall + calling convention by defining XZ_FUNC=__stdcall when building and + using the functions from XZ Embedded. |